This invention relates generally to electronic strobe light circuits and more particularly to the flash trigger circuit of an electronic strobe light in an emergency warning system. Such strobe light devices are frequently associated with audible warning devices such as horns, and provide an additional means for getting the attention of persons who may be in danger. Proper operation of the strobe light is of the utmost importance to persons in danger who are hard of hearing or deaf.
In a typical strobe light circuit of this type, the strobe light is a gaseous discharge tube, the firing of which is initiated by a trigger circuit. The flash circuit, which includes the flashtube and the trigger circuit, is typically energized from a voltage source circuit having a capacitor across its output terminals which is connected in parallel with the flash circuit. The flash occurs when the voltage across the tube exceeds the threshold firing voltage required to actuate the trigger circuit. When the flashtube is triggered, it becomes conductive and rapidly discharges the stored energy from the voltage source circuit capacitor until the voltage across the flashtube has decreased to a value at which the flashtube extinguishes and becomes nonconductive.
In one known strobe circuit of the type described above, the trigger circuit uses a SIDAC which breaks down at a predetermined voltage causing the flashtube to trigger. The relationship between the voltage across the voltage source circuit capacitor and the voltage across the SIDAC is important to the operation of the flash circuit. Ideally, the SIDAC breaks down at precisely the time when the voltage source circuit capacitor is charged with enough energy to cause the flash tube to flash with a desired light output. The voltage across the capacitor at this time is the threshold firing voltage. If the SIDAC breaks down at a later time, the capacitor will have charged beyond the energy level which the flashtube was intended to dissipate, thus causing unnecessary wear on the flashtube, as well as the voltage source circuit capacitor. Conversely, if the SIDAC breaks down before the capacitor has fully charged, the flash will be weak, an unacceptable result in a system which is designed to save lives.
The trigger circuit of the prior art provides only a single resistor to govern the relationship between the capacitor voltage and the SIDAC voltage. In an ideal circuit, the single resistor would be enough to ensure the desired linear relationship between the capacitor and SIDAC voltages. However, variances in the electrical element values, even within stated tolerances, or variances in the values due to temperature changes can cause maloperations as described above.